Gaucher disease (GD) is an autosomal recessive defect of glycosphingolipid metabolism characterized by a deficiency of the lysosomal enzyme acid b-glucosidase. The resultant accumulation of the substrate glucosylceramide, primarily in cells of monocyte/macrophage origin, leads to the clinical manifestations of anemia, thrombocytopenia, hepatosplenomegaly, skeletal disease and, less frequently, pulmonary involvement. The focus of the natural history component of this study will be to establish genotype-phenotype correlations. Several recent studies clearly demonstrate that regular intravenous infusions of placental-derived and macrophage-targeted acid b-glucosidase alglucerase (CeredaseR) result in the regression of most of the GD manifestations. However, the threshold dose for enzyme effectiveness has not been established and the ultimate impact of therapy on skeletal involvement is unknown. The treatment arm of this study will focus on defining the optimal dose schedule.